Thin panel drilling method and apparatus

ABSTRACT

The invention is directed to a method and apparatus for selectively and simultaneously drilling a plurality of holes in thin panels such as printed circuit boards, while providing for automatic changing of the drill bits, individually or plurally, as required. A tray of drill bits is driveable in X and a row of vacuum pickers are driveable in Y, so that the various bit locations of the tray are addressable by such X-Y positioning, and selectable vacuum pickers are extensible and retractable so as to pick and place the drill bits at various matrix locations of the tray. The vacuum pickers also are extensible and retractable through corresponding tray openings in order to deliver replacement bits to, and retrieve used bits from, a flipper assembly associated with each drilling module. Each flipper assembly transfers bits back and forth between the vacuum picker and drill without having to transfer either bit through the opening in a footprint portion of the pressure foot which engages the materials to be drilled during the drilling operation. Thus, the footprint opening may be made smaller in diameter than depth stop collars or the like which are of greater diameter than the working portion of the bit which is advanced through the footprint opening during drilling. This smaller footprint opening of the pressure foot is for minimizing or eliminating hole &#34;smears&#34; and for overcoming problems normally associated with the so-called &#34;oil can effect&#34;.

This application is a divisional of Ser. No. 164,840, filed Mar. 7,1988, now U.S. Pat. No. 4,932,117.

PRIOR ART CROSS-REFERENCES

U.S. Pat. No. 2,267,336--METHOD AND APPARATUS FOR FABRICATION OF SHEETMETAL COVERING PARTS--Kindelberger, issued Dec. 23, 1941.

U.S. Pat. No. 3,678,572--TOOL CHANGER--Mello et al., issued July 25,1972.

U.S. Pat. No. 4,679,296--MACHINE TOOL--Watanabe et al, issued July 14,1987.

U.S. Pat. No. 3,200,492--MULTIPLE USE MACHINE WITH TOOLCHANGER--Lehmkuhl, issued August 17, 1965.

U.S. Pat. No. 4,041,601--MACHINE TOOL WITH AN AUTOMATIC TOOLCHANGER--Schimanski, issued Aug. 16, 1977.

U.S. Pat. No. 3,276,116--TOOL CHANGER--Stark, issued Oct. 4, 1986.

U.S. Pat. No. 3,775,837--NUMERICALLY CONTROLLED MACHINE TOOL WITHAUTOMATIC TOOL CHANGING APPARATUS, issued Dec. 4, 1973.

U.S. Pat. No. 3,844,028--AUTOMATIC TOOL CHANGER--Hague et al., issuedOct. 29, 1974.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a method and apparatus for drilling aplurality of holes in sheet-like material, especially multi-ply printedcircuit board material.

One feature of the invention provides a drill bit changing arrangementwhich maintains replacement bits in an array in a supply tray locatedabove the drills so that no interference will be occasionedtherebetween. The storage capacity of the supply tray of the inventionis thus not limited by those considerations which would imposerestriction upon a supply which is required to move to locationsproximate the drill for a bit changing operation. This also allowssupply tray replacement during the drilling operation. Other features ofthe invention comprise a flipper having pockets in which bits arereceivable for lateral transfer to and from a central axis of each drillfor the bit changing operation and a vacuum tube "picker" by which thebits are transferred back and forth between the flipper and the supplytray.

Accordingly, the invention provides a bit changing arrangement whichalleviates problems of interference of the supply with the work piece orthe drill, while enhancing the bit storage capacity and drilling machineversatility.

Of the prior art cross referenced above, U.S. Pat. No. 2,267,336discloses interchangeable inserts 35 for a pressure foot 34, but thereis no provision for or suggestion of a drill bit supply and/or changingmeans therein. Even more importantly, this reference does not discloseor suggest scrap evacuation and the problems inherent therein.

Each of the other cross referenced patents discloses an individual drilland laterally displaceable tool changer for the drill, with thereplacement drill bits being stored in an adjacent endless conveyor orcarousel or a supply integral with the housing of the drill.

Other features of the invention will become apparent from the followingdisclosure.

The invention is directed to a method and apparatus for selectively andsimultaneously drilling a plurality of holes in thin panels such asprinted circuit boards, while providing for automatic changing of thedrill bits, individually or plurally, as required. A tray of drill bitsis driveable in X and a row of vacuum pickers are driveable in Y, sothat the various bit locations of the tray are addressable by such X-Ypositioning, and selectable vacuum pickers are extensible andretractable so as to pick and place the drill bits at various matrixlocations of the tray. The vacuum pickers also are extensible andretractable through corresponding tray openings in order to deliverreplacement bits to, and retrieve used bits from, a flipper assemblyassociated with each drilling module. Each flipper assembly transfersbits back and forth between the vacuum picker and drill without havingto transfer either bit through the opening in a footprint portion of thepressure foot which engages the materials to be drilled during thedrilling operation. Thus, the footprint opening may be made smaller indiameter than depth stop collars or the like which are of greaterdiameter than the working portion of the bit which is advanced throughthe footprint opening during drilling. This smaller footprint opening ofthe pressure foot is for minimizing or eliminating hole "smears" and forovercoming problems normally associated with the so-called "oil caneffect".

The replacement bits utilized in the industry for which the instantinvention is particularly applicable generally have depth stop collarsattached to the drill bits prior to their supply to the drill. Thesecollars generally are adjustably positioned along the length of thedrill bit so as to compensate for changes in the length of the bit, asmight occur upon resharpening of a bit, and thus to maintain a preferreddepth of penetration of the bit into the work. Since the drill bitsutilized in this industry generally have been changed heretofore bypassing them through the bottom hole of the pressure foot while thecollar is still attached thereto, and since the collars are larger indiameter than the drill bits, a larger footprint opening is required inthe pressure foot generally used with these drills.

Excessive burring and wicking path fractures can and do occur from the"oil can effect" on the material being drilled when the footprintopening of the pressure foot is relatively much larger than the diameterof the drill bit.

A further disadvantage of having such an enlarged hole in the bottom ofthe pressure foot is that the vacuum drawn on the pressure foot, inorder to evacuate the scrap or chad circuit board material therefrom, isnot concentrated upon the flutes of the drill bit as much as when thehole of the pressure foot is much closer to the size of the bit itself.Thus, the chad that is not removed from the flutes is transferred ontothe internal surfaces of subsequently drilled holes, so that these bitsof chad become packed at various spots along the internal diameters ofthe subsequently drilled holes.

Typically, the internal diameters of these holes have copper appliedthereto during water and chemical "electroless" baths such that watercan get in or behind the packings or so-called "smears" of chad.Ferrules of copper are then electroplated onto the initially appliedcopper, and the water behind the resin packings can cause "pops" in thefinal ferrules upon passing of the boards through subsequent reflow orwave soldering processes at which temperatures typically reach 550° F.Even if the ferrule does not pop, it is weakened sufficiently to causeelectrical failures during the subsequent expansion and contractionthereof in normal use. Further, the epoxy resin "packing" can serve asan insulator blocking a required electrical connection between internalcopper tracks of multiple layer boards and the finished copper ferrule.

Thus, there is a definite need in the industry for eliminating suchpackings or smears of chad on the inside diameters of the drilled holes.Heretofore, in order to overcome this problem, the resin portions of thehole have been etched away to a larger diameter than the copper layerportions by means of sulfuric acid or plasma or the like.

By the instant invention, drill bits are changed without passing throughthe bottom hole of the pressure foot so that the hole may be much closerin diameter to the working portion of the drill bit. Thus, there is anincreased vacuum effect in the footprint opening upon the chad caught inthe flutes of the drill bit during retraction of the bit from thematerial. Still more concentration of the vacuum in the drill flutes maybe provided by grooving or fluting the internal surface of the pressurefoot in or near the inner surface of the footprint opening so as tocause a swirling air flow.

These and other features of the instant invention and their distinctionsover the prior art will become more apparent from the following detaileddisclosure. The invention comprises several steps and the relation ofone or more of such steps with respect to each of the others and theapparatus embodying features of construction, combinations of elements,and arrangement of parts which are adapted to effect such steps, all asexemplified in the following detailed disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of the apparatus of the invention, as viewedalong the X axis.

FIG. 2 is a partial front elevation of the apparatus of the invention asviewed along the Y axis.

FIG. 3 is a partial top plan view of the device of FIG. 1.

FIG. 4 is a top plan view of the supply tray and means for moving it inthe X direction.

FIG. 5 is an enlarged portion of the supply tray of FIG. 4.

FIG. 6 is an enlarged cross section, as generally indicated by thearrows 6--6 of FIG. 4.

FIG. 7 is a top plan view of the device of FIG. 2.

FIG. 8 is a front elevation of the picker support apparatus of theinvention.

FIGS. 9 and 10 are side elevations illustrating operation of a pickerdevice during transfer of a bit to or from the supply tray.

FIG. 11 is a partial side elevation illustrating the attachment of thepicker platform to a screw used for positioning the platform along the Yaxis.

FIG. 12 is a partial cross sectional view, as generally indicated by thearrows 12--12 of FIG. 11.

FIG. 13 is a partial side elevation of a drill assembly as viewedgenerally in the direction of arrows 13--13 of FIG. 7.

FIG. 14 is a cross sectional view through a drill assembly as generallyindicated by the arrows 14--14 in FIG. 7.

FIG. 15 is a cross sectional view as generally indicated by arrows15--15 of FIG. 13.

FIG. 16 is a partial cross section of a drill assembly illustrating theraised and lowered positions of the drill.

FIG. 17 is a partial cross section illustrating the manner in which apicker is passed through an opening in the supply tray during transferof a bit to or from the flipper assembly.

FIGS. 18-21 are partial cross sections looking down into a pressure footand illustrating the various positions of the flipper during the bitchanging operation.

FIG. 22 is a partial cross section as viewed generally in the directionof arrows 22--22 of FIG. 18.

FIG. 23 is a partial cross section as viewed generally in the directionof arrows 23--23 of FIG. 19.

FIG. 24 is a partial cross section as viewed generally in the directionof arrows 24--24 of FIG. 20.

FIG. 25 is a partial cross section as viewed generally in the directionof arrows 25--25 of FIG. 21.

FIG. 26 is a top plan view of the flipper of the invention.

FIG. 27 is a cross section as generally viewed in the direction ofarrows 27--27 of FIG. 26.

FIG. 28 is a top plan view of an alternate embodiment of the flipper.

FIG. 29 is a block diagram illustrating various portions of the overallmachine and the control for them.

FIG. 30 is a power distribution block diagram for the device of theinvention.

FIG. 31 is a partial cross section through a hole in a multi-ply circuitboard, illustrating the various layers of insulating and conductingmaterials.

FIG. 32 is a partial cross section somewhat similar to that of FIG. 31after a ferrule is formed.

FIG. 33 illustrates the difference between small and large footprints ofthe pressure foot and an effect thereof.

FIG. 34 is a partial cross section further illustrating problemsinherent with a pressure foot having a large footprint.

FIG. 35 is an enlarged isometric view of a brass bushing and conicaldepression therein for guiding the vacuum tube of a picker.

FIG. 36 is an enlarged, fragmentary cross-section illustrating a passagethrough the lower housing and the guide bushing therein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, a work support table 142 is moveable in theY direction via feed screw 144 and motor 146 in a stepwise manner inorder to feed the work material underneath the banks or rows of drillassemblies 50, with each row of drill assemblies being parallel to the Xaxis of a cartesian coordinate system. Each drill assembly 50 of eachrow is individually moveable in the X direction via attachment to acable 152. Cable 152 is looped around pulleys at opposite ends of eachrow with a drive motor provided for each such cable so as to positioneach individual drill assembly in X, within limits which are readilydiscernible by reference to FIG. 7 and according to a programcorresponding to the circuit board to be drilled. Thereafter, hydraulicdrilling motors 70 (FIGS. 13 and 14) with rotating bits 74 are advancedinto drilling engagement with the circuit board material by a drillZ-axis motor 54 of each drill assembly 50. Each drill assembly issupported between two spaced longitudinal granite beams 7 which, inturn, are supported by a granite bed.

As seen in FIGS. 1 and 4, steel frame 2 supports Thompson rods 38 which,in turn, support a wheeled platform 36 that is displaceable in the Xdirection upon actuation of feed screws 44 by motors 46 in accordancewith a program subroutine directed to drill bit changing. Platform 36supports drill bit tray 42 having an array of drill bit receiving holes47 interrupted by rows of larger passages 48 through the tray and whichcorrespond the rows of drill assemblies 50.

Positioned above the supply tray 42 is a wheeled "picker" carriage 10that is displaceable in the Y direction by means of electric motor 6 andfeed screw 8, also under control of the drill bit replacement subroutineof the program. As seen in FIGS. 1, 3, and 8-10, the carriage hasvertical fluid jacks 14 supporting a horizontal cross bar 16 accordingto actuation of jacks 14. Vertically depending posts 18 are attached tocross bar 16 and provide suspended support of platform 22 on which a rowof vacuum picker modules 20 are mounted.

Each picker module comprises a base 23 and a vertical guide rod 26supported thereon by a bracket 24. A slide 30 is moveable up and downguide rod 26 according to actuation of a pneumatic cylinder 28, withslide 30 providing suspended support of a vacuum spindle or tube 32therefrom. Vacuum tube 32 is telescopic within a guide tube 34 which isalso fixed to and extends through platform 22. Thus, all of the pickermodules 20 are displaceable in unison in the Z direction by actuation offluid jacks 14; and the vacuum tube 32 of an individual picker module 20is selectively extensible and retractable relative to platform 22according to actuation of a corresponding pneumatic cylinder 28.

Thus, the X movement of wheeled platform 36 and Y movement of wheeledcarriage 10 allows alignment between each vacuum picker tube 32 and agreat many locations on tray 42 to facilitate selective picking andplacing of drill bits at these locations. A further description of thisapparatus in operation will be provided in the following disclosure.

The reader's attention now is directed to FIGS. 13-15 for anunderstanding of the structure which provides vertical displacement ofthe drills 70 in the Z direction and horizontal displacement of thedrill assemblies in the X direction. Each drill assembly is supportedand retained between two granite beams 7 by means of angled flanges 80of a lower housing assembly 78, with air bearings provided between thegranite beams 7 and flanges 80 for smooth ride of the drill assemblies50 along the granite beams 7. As indicated earlier, cable 152 is loopedaround pulleys on opposite ends of the granite beams and the top run ofeach cable 152 (FIG. 13) is attached to a corresponding lower housing 78in order to horizontally displace the drill assembly 50 upon actuationof a cable driving motor (not shown) and according to a control program,with the position of each drill assembly 50 in the X direction beingmonitored by encoder strips 156 and a reader 158 (FIG. 15).

Upper housing portion 76 is attached to lower housing 78 and providedwith large openings in the circumference thereof allowing ease of accessto the normal hydraulic fittings and tubing at or near the top ofhydraulic drill 70. A pulley 58 is keyed to shaft 59 which is rotatablysupported within upper housing 76 by bearing assembly 61, and timingbelt 56 provides a driving connection between pulley 58 and a motor 54for raising and lowering drill module 70. A ball screw 62 is coaxialwith the longitudinal axis 52 of drill assembly 50 and is displaceabletherealong by means of a ball nut 64 attached to pulley 58 for rotationtherewith upon actuation of motor 54. As seen in FIG. 14, the drillingmodule 70 is suspended from the lower end of ball screw 62 by universalconnector 68 in order to compensate for any misalignment between ballscrew 62 and the longitudinal axis 52 of drill module 70.

A pressure foot 90 depends from each drill assembly 50 by attachment at108 to a pair of rods 106 which are slidably received within lowerhousing 78 (FIG. 14). Upper rods 100 are attached to rods 106 by apneumatic piston/cylinder arrangement 110 and are slidably receivedwithin ears 77 (FIG. 14) of upper housing 76. A compression spring 104is sandwiched between the top surface of each ear 77 and a nut 102threaded to the top end of a rod 100. Thus, pressure foot 90 issuspended from the top of housing 76 on compression springs 104 whendrill module 70 is raised to the position of FIG. 14.

As seen in FIGS. 15, 35, and 36, lower housing 78 includes a tubularpassage through the length thereof at 86; and a brass bushing 87 (FIGS.35 and 36) having a conical depression in the top portion thereof issituated at the top and bottom of the passage 86 so as to provide atapered leading on top of each bushing and thus guide and preciselyalign picker tube 32 as it is extended into and through passage 86.

A flipper rotation motor 134 (FIG. 13) is also attached to upper housing76, with rod 132 depending downwardly through and rotational withinlower housing 78 according to actuation of motor 134. At the lower endof rod 132, is attached a flipper 111 for laterally transferring drillbits back and forth between the collet 72 (FIG. 25) of drill module 70and the vacuum tube 32 that is extendable through passage 86 of lowerhousing 78.

As seen in FIG. 26, the flipper 111 comprises a main body 112 attachedby set screw 114 to the lower end of support rod 132 and has an openingtherein defining a "replacement bit" pocket 116 with an O-ring 118 (FIG.27) therein to slightly grip the collar of a replacement bit receivedtherein. A split, "used bit" pocket 120 comprises cooperating portionsof body 112 and a jaw 122 which is pivotally attached to body 112 atpivot point 126. As seen in FIG. 27, pivotal jaw 122 is provided withportion 124 having a beveled flange, as well as a vertical protrusion130 (as seen, for instance, in FIGS. 23 and 26). The functions of theseportions of jaw 122 will be explained in the following disclosure.

An alternate embodiment of the flipper assembly is illustrated in FIG.28 wherein the body has two complete pockets therein with the "used" bitpocket having two cooperating jaws 97 and 99 positioned thereabove andactuatable in unison. Each jaw has a beveled portion similar to portion124 of FIG. 27 and for substantially the same purpose, i.e., holdingcollar 72 during removal of a bit from a drill.

OVERALL OPERATION OF THE MACHINE

Referring to FIGS. 2 and 7, the work to be drilled may be totallypositioned under all of the drill assemblies 50 or may be incrementallyadvanced in the direction Y, according to the number of holes to bedrilled in the board and the positioning thereof. In either event, eachdrill assembly 50 is shiftable in X, to establish the point in the X-Yplane of the work at which it will drill a hole. Thus, each drill candrill one or more holes in the work as required. Periodically duringoperation of the machine it is necessary to replace a worn or brokendrill bit 74, and the instant invention particularly provides forefficient rapid changing of such drill bits.

When it is necessary to replace one or more drill bits, picker carriage10 and tray platform 36 are relatively positioned in X and Y forpositioning the appropriate replacement bit in line with a picker vacuumtube 32. At least one of the vacuum tubes 32 is telescoped out of itssupport 34 by actuation of cylinder 28 (as seen in FIGS. 8-10), and theappropriate replacement bit is gripped by vacuum and retrieved byretracting the vacuum tube 32 back into its support 34. Thereafter, trayplatform 36 is driven in X to a "home" position so as to position atleast one row of tray openings 48 directly above a corresponding row ofdrill assemblies 50, with all of the drill assemblies 50 of that rowalso returned to a "home" position into alignment with overhead openings48 of the supply tray 42. Then, as seen in FIGS. 8 and 17, cylinders 14may be actuated to lower platform 22 with all of the vacuum pickermodules 20 in unison such that guide tubes 34 of the picker modules 20pass through openings 48 and tray 42 and are lowered to a position justabove, or into engagement with, passages 86 of each corresponding drillassembly lower housing 78.

At this time or prior hereto, drill module 70 is raised by actuation ofmotor 54 and flipper assembly 111 is pivoted counterclockwise (CCW) asviewed in FIG. 18 by motor 134 to position split pocket 120 in line withthe drill bit 74. Drill module 70 is lowered again such that the collar75 of drill bit 74 engages the beveled portion of member 124 and openspivotal jaw 122 against the bias of spring 128. Once collar 75 hascompletely cleared the bevel of portion 124, the collet of drill 70 isopened to release bit 74 and drill module 70 is raised clear of thedrill bit 74. Referring to FIGS. 18 and 22, the jaw 122 of the flipperis biased closed by spring 128 so that portion 124 extends over the topof drill bit collar 75 to ensure that the bit is retained in pocket 120during raising of drill module 70.

Thereafter, as seen in FIGS. 19 and 23, flipper 110 is pivoted clockwise(CW) sufficiently to align pocket 116 with passage 86 for insertiontherein of the replacement bit by vacuum nozzle 32. The O-ring 118 (FIG.27) retains the replacement bit in pocket 116.

Upon sufficient retraction of vacuum nozzle 32 by cylinder 28, flipper110 is rotated CW further to align split pocket 120 with passage 86 (asseen in FIGS. 20 and 24) and a vertical protrusion 130 of jaw 122engages a stop member 88 depending from housing 78 to open the jaw, asseen in FIG. 20. Thus, the member 124 is cleared from the top of thedrill bit collar and the used bit may be retrieved from pocket 120 byextension and retraction of vacuum nozzle 32.

A slot 98 (FIGS. 16 and 18-25) may be provided in pressure foot 90 inorder to minimize clearance required to pass a drill bit through theside wall of pressure foot 90. FIGS. 18-21 also reveal a phantom-linedopening 96 through the side wall of pressure foot 90 so that scrap orchad may be evacuated by vacuum (as discussed earlier) in the directionindicated by arrows.

Flipper assembly 111 is then pivoted CCW to align pocket 116 with the Zaxis 52 and the drill module 70 is lowered to grip the replacement drillbit 74 in collet 72 and, upon re-raising drill module 70 with thereplacement bit, flipper assembly 111 is pivoted back to the positionillustrated in FIG. 19 and out of the path of the drill module 70.

Once the used bit has been grasped by vacuum nozzle 32 as illustrated inFIG. 24, the cylinders 14 may be actuated to raise platform 22 with allof the picker modules 20 thereon to the position of FIG. 8, whereuponthe earlier described X-Y positioning between supply tray 42 and thevacuum nozzle 32 is performed and nozzle 32 is extended to place theused bit in a vacant location on the tray 42.

During raising and lowering of drill module 70, a tie bar 66 (FIG. 14)attached to ball screw 62 is also raised and lowered. During lowering,tie bar 66 engages the upper end of cylinders 110 to push pressure foot90 into engagement with the work (against the upward biasing of springs104 at the top of rods 100). The amount of pressure applied to the workis adjustable via the air pressure supplied to cylinders 110. Forinstance, the air pressure on a prototype was adjustable between 10-30psi and set for a nominal value of 20 psi.

As discussed earlier; the footprint at which pressure is applied to thework by pressure foot 90 can have a profound effect upon the quality ofthe holes being formed in the work to which the invention is directed,and the reader's attention is particularly directed to FIGS. 31-34 for abetter understanding of the particular problems involved As seen in FIG.31, the work may comprise alternating layers of copper 162 and anonconductive resin 164 or the like defining a so-called "stack" ormulti-layer circuit board 160 through which the holes are to be drilled.

Even though it is standard practice to use an aluminum or aluminum-cladoverlay material 170 (FIG. 34) on top of the "stack" so as to reducedisruption of the planarity of the layers of stack 160 during suchdrilling, the overlay material and/or work can experience the "oil caneffect" illustrated in FIG. 33 when the pressure foot is provided with arelatively large footprint hole so that the drill bits can be changed bypassing through the lower pressure foot opening. This "oil can effect"can result in burring of the "stack" and/or the formation of wickingpaths between the layers of the stack, especially during withdrawal ofthe drill bit from the work.

Another problem inherent in the industry involved is that of resin"chad" being transferred to a subsequently drilled hole via the flutesof the drill bit. Although it is typical of the prior art to draw avacuum on pressure foot 90 in order to remove the scrap, such transferalof chad and so-called "smears" or packings still occur on the interiorof subsequently drilled holes from the flutes of the drill bit. Thesesmears are non-uniformly distributed over the internal diameter of thehole and can result in the earlier described problems of ferrule "pops"and/or blocking of conductivity between various copper layers 162 andthe non-electrically applied copper, as well as the subsequentlyelectroplated copper ferrule. However, by the instant invention, thevacuum effect on the flutes of the drill bit are increased at theopening of the pressure foot. Various sized inserts 92 (FIG. 16) may beutilized according to the drill bit diameters and the nature of the workso as to overcome these above described deficiencies. O-ring 94 may beused to retain inserts 92 in pressure foot 90.

Having described the invention, it may be seen that the objects setforth above, among those made apparent from the preceding description,are efficiently obtained and, since certain changes may be made incarrying out the above method and in the construction set fort withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpereted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the inventionhereindescribed, and all statements of the scope of the invention which,as a matter of language, might be said to fall therebetween.

We claim:
 1. In a method of drilling holes in thin panel material with drill bits having enlarged portions said method comprising the steps of applying pressure to said material via a pressure foot surface defining a footprint and generally surrounding and proximate each hole during drilling thereof in order to minimize disruption of a planarity of said material by a drill bit, said drill bit passing through a hole of said footprint during said drilling, and removing said bit from a drill and replacing it with new bit as required, the improvement comprising the steps of:providing said footprint hole with a diameter less than that of said enlarged portions of said drill bits in order to further minimize said planarity disruption by use of said pressure foot; and retaining said pressure foot hole and drill generally coaxial while performing said removing and replacing without passing said enlarged portions of said bits through said footprint hole.
 2. The improvement of claim 1, wherein said method further comprises a step of evacuating chad, produced during said drilling, from within said pressure foot by means of vacuum, and further comprising the step of:improving said evacuating by minimizing said pressure foot hole diameter.
 3. The improvement of claim 2, and further comprising the step of:providing fluting within said pressure foot so as to provide vortex suction action for improved evacuation of said chad.
 4. The improvement of claim 1, and further comprising the steps of:providing a supply tray of replacement bits above said drill; and replacing said supply tray during said drilling.
 5. The improvement of claim 1, and further comprising the steps of:providing plural rows of drills each positionable relative to an assigned hole location of said thin panel material; selectively moving said panel material and individual ones of said drills relative to each other in X and Y in order to accomplish said positioning; and selectively moving said drills in Z in order to accomplish said hole drilling.
 6. The improvement of claim 5, and further comprising the steps of:providing a supply of replacement bits situated above and in non-interfering relation with said drills; providing at least one vacuum picker; positioning said picker and supply relative to each other according to a selected new bit to be retrieved from said supply and retrieving the selected bit; repositioning said picker and supply relative to each other and aligning said picker with a corresponding hole through said supply tray; extending said picker in Z through said tray and transferring said new bit to a flipper means for laterally transferring said new bit to said drill; and performing said transferring.
 7. The improvement of claim 6, and further comprising the steps of:retrieving a used bit from said drill via said flipper means; and retrieving said used bit from said flipper means by said picker. 